Several techniques have been used to reduce the open circuit voltage of an arc welding power source before the welder is to be used for a welding process. One of the most common designs is a control circuit that reduces the conduction period of the output switching devices, so the open circuit voltage is retained at a desired lower value. In an inverter type power source, the switching devices are usually in the form of field effect transistors (FETs) or insulated gate bi-polar transistors (IGBTs). Since the switching frequency is usually greater than 20 kHz, the conduction period of these switching devices is very short and depends upon the operating frequency of the inverter. In order to reduce the open circuit voltage to a low level, the minimum conduction period of the switching devices requires a complicated and electrically demanding control circuit. Power sources employing such open circuit voltage (OCV) control devices also include a circuit to release the control of the power source to allow the welding power to be obtained during welding. Such detection devices with releasing circuits are usually prone to noise and sensitivity problems.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such approaches with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.